Polymers having broad molecular weight distributions and methods of making the same

ABSTRACT

Methods of polymerizing at least one olefin include contacting the olefin with a catalyst comprising chromium and with a cocatalyst comprising a non-transition metal cyclopentadienyl (Cp) compound. The polymerization may be performed in the presence of hydrogen. Using the cocatalyst in conjunction with the catalyst increases several properties, such as the high load melt index (HLMI), the M W , and the M N , of the polymers produced by this polymerization method. Polymer compositions produced by such methods have various unique properties, including a PDI greater than about 30. Additional embodiments include articles of manufacture or end use articles formed from such polymer compositions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional Application of U.S. patent application Ser. No.11/929,448 filed Oct. 30, 2007, published as US 2008-0051545A1, which isa divisional application of U.S. patent application Ser. No. 10/829,842,issued as U.S. Pat. No. 7,307,133 on Dec. 11, 2007, all entitled“Polymers Having Broad Molecular Weight Distributions and Methods ofMaking the Same.” The present application is related to U.S. Pat. No.6,977,235, issued on Dec. 20, 2005 and entitled “Catalyst SystemComprising a Chromium Catalyst and a Non-Transition MetalCyclopentadienyl Cocatalyst.” Each of the patents and patent applicationis hereby incorporated by reference herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

FIELD OF THE INVENTION

The present invention generally relates to polymers, and moreparticularly to polymers having relatively broad molecular weightdistributions and methods of making the same using a chromium-basedcatalyst and a non-transition metal cyclopentadienyl cocatalyst.

BACKGROUND OF THE INVENTION

The production of polyolefins using chromium-based catalysts is wellknown in the art. Various supports have been employed for suchchromium-based catalysts. Silica supports have primarily been used dueto their ability to form highly active polymerization catalysts. Otherexamples of supports that have been used for such chromium-basedcatalysts include alumina and aluminophosphates. Supportedchromium-based catalysts were initially employed in solutionpolymerization processes. However, slurry polymerization soon becameknown as the more economical route to many commercial grades ofpolyolefins using such catalysts.

A polyolefin exhibits various physical, and in particular, mechanicalproperties that are highly affected by its molecular weight distribution(MWD). The molecular weight distribution can be determined by means of acurve obtained by gel permeation chromatography (GPC). It can bedescribed by a parameter known as the polydispersity index (PDI), whichindicates the breadth of the molecular weight distribution and isequivalent to the weight-average molecular weight of a polymer dividedby the number-average molecular weight of the polymer (i.e.,M_(W)/M_(N)). A broadening in the molecular weight distribution of apolyolefin tends to improve the flow of the polyolefin when it is beingprocessed at high rates of shear.

The polymerization of olefins using chromium-based catalysts is oftenperformed in the presence of hydrogen to produce polyolefins havingrelatively low molecular weights. However, although hydrogen can be usedto regulate the molecular weight, the breadth of the molecular weightdistribution of a polyolefin tends to be limited by the choice ofcatalyst. A need therefore exists to broaden the molecular weightdistributions of polyolefins produced using chromium-based catalysts.

SUMMARY OF THE INVENTION

Methods of polymerizing at least one olefin include contacting theolefin with a catalyst comprising chromium and with a cocatalystcomprising a non-transition metal cyclopentadienyl (Cp) compound. Thepolymerization may be performed in the presence of hydrogen. Using thecocatalyst in conjunction with the catalyst increases severalproperties, such as the high load melt index (HLMI), the M_(W), and theM_(N), of the polymers produced by this polymerization method.

Polymer compositions produced by such methods have various uniqueproperties. In one embodiment, the polymer compositions have a M_(W)greater than about 600,000 g/mol and a HLMI in a range of from about0.01 g/10 min to about 10 g/10 min. In another embodiment, the polymercompositions have a M_(W) greater than about 400,000 g/mol and a zeroshear viscosity (E_(o)) less than about 10⁸ Pa·s. In yet anotherembodiment, the polymer compositions have a rheological breadthparameter greater than about 0.15 and a PDI greater than about 30.Additional embodiments include polymer compositions having otherproperties, and articles of manufacture or end use articles formed fromthe foregoing polymer compositions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a graph illustrating the molecular weight distributionsof polyethylene resins formed using a chromium-based catalyst anddifferent non-transition metal cyclopentadienyl cocatalysts and of apolyethylene resin formed using a chromium-based catalyst but nococatalyst.

FIG. 2 depicts a graph illustrating the molecular weight distributionsof polyethylene resins formed using a chromium-based catalyst anddifferent concentrations of a dicyclopentadienyl magnesium cocatalystand of a polyethylene resin formed using a chromium-based catalyst and atriethylaluminum cocatalyst.

FIG. 3 depicts a graph illustrating the molecular weight distributionsof two polyethylene resins formed using a chromium-based catalyst,wherein one is formed with a cyclopentadienyl lithium cocatalyst and oneis formed without a cocatalyst.

DETAILED DESCRIPTION OF THE INVENTION

A catalyst system suitable for use in polymerizing olefins includes atleast one chromium-based catalyst and at least one non-transition metalcyclopentadienyl (Cp) compound as a cocatalyst. A mole ratio of thenon-transition metal Cp compound to the chromium in the catalyst systemmay range from about 0.001 to about 20, from about 0.001 to about 10,from about 0.003 to about 20, from about 0.01 to about 3, or from about0.02 to about 2. The non-transition metal Cp compound typicallyconstitutes from about 0.01 to about 50 ppm by weight of the reactionzone contents, alternatively from about 0.1 to about 20 ppm, oralternatively from about 0.1 to about 10 ppm by weight of the contentsof a reaction zone in which the catalyst system is used forpolymerization.

The non-transition metal Cp cocatalyst contains a non-transition metalbonded to a Cp group. Examples of suitable non-transition metals includea Group I metal such as lithium (Li) and sodium (Na), a Group II metalsuch as magnesium (Mg), and a Group III metal such as aluminum. Examplesof suitable Cp groups include cyclopentadienyl, a fluorenyl group, andan indenyl group. The Cp group may be substituted or unsubstituted. Forexample, the Cp group may be substituted with an alkyl group, an arylgroup, an alkylaryl group, an alkoxy group, an aryloxy group, analkylsilyl group, or combinations thereof. In an embodiment, the metalCp cocatalyst is cyclopentadienyl lithium (CpLi), dicyclopentadienylmagnesium (Cp₂Mg), a lithium aluminum cyclopentadienyl trialkyl, orcombinations thereof. If the metal is a divalent or trivalent metal,other anions may accompany the Cp group, such as halides, alkoxides, ororganic radicals. For example, the metal Cp cocatalyst may also becyclopentadienyl magnesium ethoxide (CpMgOC₂H₅), indenyl aluminumdibutyl (IndAl(C₄H₉)₂) or fluorenyl ethyl boron chloride (FluBClC₂H₅).The metal Cp cocatalyst may also be a complex salt of two metals such aslithium aluminum cyclopentadienyl triethyl (LiAlCp(C₂H₅)₃).

The chromium-based catalyst includes chromium on a support that servesas a carrier for the chromium. The support may primarily include aninorganic oxide such as silica, alumina, aluminophosphates, and mixturesthereof. In an embodiment, the support contains greater than about 50percent (%) silica, alternatively greater than about 80% silica, byweight of the support. The support may further include additionalcomponents that do not adversely affect the catalyst system, such astitania, zirconia, alumina, boria, thoria, magnesia, and mixturesthereof. The support has a specific surface area and a specific porevolume effective to provide for an active catalyst. A QuantachromeAutosorb-6 Nitrogen Pore Size Distribution Instrument, which iscommercially available from the Quantachrome Corporation of Syosset,N.Y., may be used to determine the specific surface area (hereinafter“surface area”) and specific pore volume (hereinafter “pore volume”) ofthe support. The surface area of the support may range from about 100square meters per gram (m²/g) to about 1,000 m²/g, alternatively fromabout 200 m²/g to about 800 m²/g, or from about 250 m²/g to about 700m²/g. Further, the pore volume of the support, i.e., an indicator of theamount of liquid it can absorb, may range from about 0.5 cubiccentimeters per gram (cc/g) to about 3.5 cc/g or alternatively fromabout 0.8 cc/g to about 3 cc/g.

The chromium may be loaded on the support using any method known in theart. In one embodiment, a coprecipitated cogel of chromium and of one ormore support components is made. As used herein, cogel refers to theproduct resulting from the gelation of two or more components. Inanother embodiment, the support is impregnated with an aqueous solutioncontaining a water-soluble chromium compound. Examples of water-solublechromium compounds include chromium oxide, chromium trioxide, chromiumacetate, chromium nitrate, or combinations thereof. In yet anotherembodiment, the support is impregnated with a hydrocarbon solution inwhich a chromium compound is dissolved after removing water from thesupport by, e.g., spray dying or azeotropically drying it. Examples ofhydrocarbon soluble chromium compounds include tertiary butyl chromate,a diarene chromium compound, biscyclopentadienyl chromium(II), chromiumacetylacetonate, or combinations thereof. The amount of chromium presentin the ensuing catalyst may range from about 0.01% to about 10% byweight of the catalyst, alternatively from about 0.2% to about 5%, orfrom about 0.5% to about 2%.

In an embodiment, chromium-based catalyst grades 963, 964, 969, orcombinations thereof may be obtained from any commercial source such asthe Grace Davison catalysts of W.R. Grace & Company of Columbia, Md.Especially suitable are those catalysts comprising chromium oxidesupported by a high porosity silica-titania as are described in U.S.Pat. Nos. 3,887,494 and 3,119,569, both of which are incorporated byreference herein in their entirety. By way of example, the support maybe produced by simultaneous gellation of silica, titania, and chromia.Such gellation may be performed by contacting an alkali metal silicatesuch as sodium silicate with an acid solution containing a titanium saltsuch as a sulfuric acid titanyl sulfate solution containing chromium,thereby forming a cogel, also known as a hydrogel. After gellation, thecogel may be aged at a pH of from about 7 to about 8 for several hoursat 80° C. It may then be azeotropically dried in an organic solvent suchas hexanol to form a xerogel. The titanium content of this support mayrange from about 1% to about 10% by weight of the catalyst. The surfacearea of this support is typically about 550 m²/g, and the pore volume ofthe support is typically in the range of from about 2.2 cc/g to about2.5 cc/g.

Additional disclosure regarding chromium-based catalysts supported bysilica/titania can be found in the following patents: U.S. Pat. Nos.4,405,501 and 4,436,886 which relate to the aging process; U.S. Pat.Nos. 4,436,883 and 4,392,990 which relate to N₂ calcination; U.S. Pat.Nos. 4,081,407 and 4,152,503 which relate to azeotropic drying usinghexanol; U.S. Pat. No. 4,981,831; U.S. Pat. Nos. 4,294,724, 4,382,022,4,402,864, and 4,405,768, and 4,424,320 which relate to titanation; andU.S. Pat. Nos. 2,825,721, 4,382,022, 4,402,864, 4,405,768, 3,622,521,3,625,864 which relate to silica-titania, all of the foregoing patentsbeing incorporated by reference herein in their entirety.Aluminophosphate supported catalysts are described in U.S. Pat. Nos.4,364,842, 4,444,965, 4,364,855, 4,504,638, 4,364,854, 4,444,964,4,444,962, each of which is incorporated by reference herein in itsentirety. Phosphated alumina supported catalysts are described U.S. Pat.Nos. 4,444,966, 4,397,765, and 4,900,704, each of which is incorporatedby reference herein in its entirety.

The chromium-based catalyst may be activated using any known techniqueafter introducing the chromium to the support. In one embodiment, thecatalyst is activated via calcination by heating it in an oxidizingenvironment. For example, the support may be heated in the presence ofair at a temperature in the range of from about 400° C. to about 1,000°C., alternatively from about 600° C. to about 900° C. Optionally, thecalcination may be followed by a reduction step. The reduction step maybe performed by, for example, heating the support in the presence ofcarbon monoxide (CO) at a temperature in the range of from about 200° C.to about 800° C. In another embodiment, the catalyst is activated via areduction and reoxidation process. Suitable reduction and reoxidationprocesses are disclosed in U.S. Pat. Nos. 4,151,122, 4,177,162,4,247,421, 4,248,735, 4,297,460, 4,397,769, 4,460,756, 4,182,815,4,277,587, each of which is incorporated by reference herein in itsentirety.

In an embodiment, the non-transition metal Cp cocatalyst is co-supportedwith the chromium-based catalyst. The metal Cp cocatalyst is loaded ontothe support after activating it. The Cp cocatalyst may be combined withthe support by, for example, impregnating the already activatedchromium-based catalyst with an organic (preferably hydrocarbon)solution comprising the metal Cp cocatalyst. The resulting Cr/metal Cpcatalyst may then be fed to a polymerization reactor. In anotherembodiment, the activated chromium-based catalyst and the non-transitionmetal Cp are separately fed to a polymerization zone. In yet anotherembodiment, the Cr catalyst and Cp compound can both be continuously fedinto a contacting vessel where they react for a period of from about 1minute to about 10 hours, and from there the contacted ingredients arefed into the polymerization zone. The two feeds can thus be accuratelyand continuously controlled during the polymerization to determine thecorrect molar Cp/Cr ratio which in turn controls polymer properties. Inthis way adjustments to the catalyst-cocatalyst recipe can be made asthe polymers are produced.

Polymer compositions may be formed by polymerizing at least one monomerin the presence of the foregoing catalyst system comprising achromium-based catalyst and a non-transition metal Cp cocatalyst.Examples of suitable monomers include unsaturated hydrocarbons havingfrom 2 to 20 carbon atoms such as ethylene, propylene, 1-butene,1-pentene, 1-hexene, 3-methyl-1-butene, 4-methyl-1-pentene, 1-heptene,1-octene, 1-nonene, 1-decene, and mixtures thereof. The chromium-basedcatalyst is particularly suitable for producing polyethylenehomopolymers, and copolymers of ethylene monomer and 1-hexene comonomer.The polymer density of such copolymers may be controlled by varying thecomonomer to monomer ratio in the reactor.

Any suitable polymerization methods known in the art may be used, suchas solution polymerization, slurry polymerization, and gas phasepolymerization. Any polymerization reactor known in the art that iscapable of polymerizing olefin monomers to produce the homopolymers orcopolymers described herein also may be used. Such reactors can compriseslurry reactors, gas-phase reactors, solution reactors or anycombination thereof. Gas phase reactors can comprise fluidized bedreactors or tubular reactors. Slurry reactors can comprise verticalloops or horizontal loops. Solution reactors can comprise stirred tankor autoclave reactors. Such reactors can be combined into multiplereactor systems operated in parallel or in series.

Any manner known in the art may be employed to contact the monomer withthe catalyst in the reaction zone. As mentioned previously, thecocatalyst may be co-supported with the catalyst, or it mayalternatively be separately introduced to a reaction zone. Suitablecontact methods include fluidized bed, gravitating bed, and fixed bedmethods. In one embodiment, the catalyst and the cocatalyst streams areboth continuously fed into a pre-contacting reaction zone prior toadding the mixture into the polymerization reactor. In thispre-contacting reaction zone, the two components react with each otherat temperatures ranging from about −10° C. to about 100° C. duringresidence times typically ranging from about 1 minute to about 2 hours.After the two components have contacted each other for the specifiedduration, the combination is then fed continuously into thepolymerization reactor.

In one embodiment, the polymerization is carried out using a pluralityof stirred tank reactors either in series, parallel, or combinationsthereof. Different reaction conditions may be used in the differentreactors. In another embodiment, the polymerization is conducted in aloop reactor using slurry polymerization. Suitable loop reactors aredisclosed in U.S. Pat. Nos. 3,248,179, 5,565,175 and 6,239,235, whichare incorporated by reference herein in their entirety. Within the loopreactor, the catalyst and the cocatalyst are suspended in an inertdiluent and agitated to maintain them in suspension throughout thepolymerization process. The diluent is a medium in which the polymerbeing formed does not readily dissolve. In an embodiment, the diluent isisobutane in which the polymer tends to swell less than in otherdiluents. It is understood that other diluents may be utilized as deemedappropriate by one skilled in the art. In an embodiment in whichethylene is polymerized in the loop reactor, the amount of ethylenepresent is in the range of from about 1% to about 20% by the weight ofthe diluent, or alternatively from about 3% to about 8%. When acomonomer such as 1-butene or 1-hexene is used, it is added to thereactor in an amount sufficient to yield a polymer having a desireddensity, which is usually in the range of from about 0.92 to about 0.96g/cc. In a loop reactor this amount is typically in the range of fromabout 0.1% to about 20% by weight of the diluent.

The slurry polymerization conditions are selected to ensure that thepolymer being produced has certain desirable properties and is in theform of solid particles. The polymerization is desirably carried outbelow a temperature at which the polymer swells or goes into solution.For example, the polymerization temperature may be less than about 110°C., alternatively in the range of from about 85° C. to about 110° C. Thecatalyst system is contacted with the at least one monomer at a pressuresufficient to maintain the diluent and at least a portion of the monomerin the liquid phase. That is, the pressure within the loop reactor maybe maintained in the range of from about 110 psi to about 700 psi orhigher. Suitable slurry polymerization processes are disclosed in U.S.Pat. Nos. 4,424,341, 4,501,855, and 4,613,484, 4,589,957, 4,737,280,5,597,892, and 5,575,979, each of which is incorporated by referenceherein in its entirety. The activity and the productivity of thecatalyst system are relatively high. As used herein, the activity refersto the grams of polymer produced per gram of solid catalyst charged perhour, and the productivity refers to the grams of polymer produced pergram of solid catalyst charged.

Additional details regarding chromium-based catalysts and/or slurrypolymerization processes can be found in U.S. Pat. Nos. 3,887,494,3,900,457, 3,947,433, 4,053,436, 4,081,407, 4,151,122, 4,294,724,4,296,001, 4,345,055, 4,364,839, 4,364,841, 4,364,842, 4,364,854,4,364,855, 4,392,990, 4,397,765, 4,402,864, and 4,405,501, each of whichis incorporated by reference herein in its entirety.

According to an embodiment, hydrogen (H₂) may be introduced to thepolymerization reaction zone to control molecular weight. The H₂ may beemployed at concentrations of equal to or less than about 3 mole % basedon the total number of moles of the diluent in a loop reactor,alternatively from about 0.1 mole % to about 2 mole %. Polymerizing theolefin in the presence of the cocatalyst and the hydrogen broadens themolecular weight distribution of the polymer and generally improves theproperties of the polymer. For example, the use of the cocatalyst inconjunction with the hydrogen results in an increase in the melt index(MI) and the high-load melt index (HLMI) of the polymer produced,whereas the MI and the HLMI of the polymer drop when the cocatalyst isused without any hydrogen present. Without intending to be limited bytheory, it is believed that the presence of the cocatalyst causes thesites on the catalyst that usually produce low molecular weight polymerto convert to chromocenyl sites that reject the comonomer, e.g., hexene,and are more sensitive to H₂.

When the metal Cp cocatalyst is included in the catalyst system added tothe reactor in the presence of hydrogen, the weight average molecularweight (M_(W)) of the polymer formed therein increases while the numberaverage molecular weight (M_(N)) decreases substantially, as compared tousing the same catalyst system run under the same reactor conditions inthe presence of the same amount of hydrogen, but without the metal Cpcocatalyst. Typically, the M_(W) may increase by equal to or greaterthan about 25%, alternatively by equal to or greater than about 50%, oralternatively by equal to or greater than about 80%. Increases of equalto or greater than about 100% also may result, depending on the catalysttype and the amount of hydrogen and metal Cp catalyst used. Further, theM_(N) may decrease by equal to or greater than about 20%, alternativelyby equal to or greater than about 40%, alternatively by equal to orgreater than about 50%, or alternatively on occasion by equal to orgreater than about 60%.

Likewise, the MI and HLMI of the polymer produced increase when themetal Cp cocatalyst is added to the reactor to which hydrogen is alsoadded, as compared to the same polymer made with the same catalyst underthe same reactor conditions but in the absence of the metal Cpcocatalyst. The MI or HLMI typically increases by equal to or greaterthan about 50%, alternatively by equal to or greater than about 100%, oralternatively by equal to or greater than about 500%. They may evenincrease by equal to or greater than ten fold, depending on the catalysttype, the amount of metal Cp cocatalyst used, and the amount of hydrogenused.

Polymer compositions or resins produced using the chromium-basedcatalyst in conjunction with the non-transition metal Cp cocatalyst haveunique properties. Examples of the polymer compositions includepolyethylene homopolymers and copolymers of ethylene monomer and1-hexene comonomer. For example, the polymer compositions have aweight-average molecular weight greater than about 100,000 g/mol.Alternatively, the M_(W) may be greater than about 250,000 g/mol,greater than about 400,000 g/mol, greater than about 500,000 g/mol, orgreater than about 600,000 g/mol. Also, the polymer compositions havebroad MWD's as indicated by PDI values greater than about 20. In someembodiments, the polymer compositions have PDI values, greater thanabout 30, greater than about 40, greater than about 50, greater thanabout 70, or greater than about 90.

The molecular weights and the molecular weight distributions of thepolymer compositions are obtained using a Waters 150 CV gel permeationchromatograph with trichlorobenzene (TCB) as the solvent using a flowrate of 1 mL/min at a temperature of 140° C. The TCB is stabilized using2,6-Di-t-butyl-4-methylphenol (BHT) at a concentration of 1.0 g/L. Aninjection volume of 220 microliters is used with a nominal polymerconcentration of 0.3 g/L at room temperature. The polymer sample isdissolved in stabilized TCB by heating it at about 160 to 170° C. for 20hours while performing occasional gentle agitation. The gel permeationchromatograph includes two Waters HT-6E columns (7.8 mm×300 mm). Thecolumns are calibrated with a broad linear polyethylene standard(Phillips Marlex® BHB 5003 resin) for which the molecular weight hasbeen determined.

Rheological breadth refers to the breadth of the transition regionbetween Newtonian and power-law type shear rate for a polymer or thefrequency dependence of the viscosity of the polymer. The rheologicalbreadth is a function of the relaxation time distribution of a polymerresin, which in turn is a function of the resin molecular structure orarchitecture. Assuming the Cox-Merz rule, the rheological breadth may becalculated by fitting flow curves generated in linear-viscoelasticdynamic oscillatory frequency sweep experiments with a modifiedCarreau-Yasuda (CY) model, which is represented by the followingequation:

$E = {E_{o}\left\lbrack {1 + \left( {T_{\xi}\overset{.}{\gamma}} \right)^{a}} \right\rbrack}^{\frac{n - 1}{a}}$

where

E=viscosity (Pa·s)

{dot over (γ)}=shear rate (1/s)

“a”=rheological breadth parameter

T_(ξ)=relaxation time (s) [describes the location in time of thetransition region]

E_(o)=zero shear viscosity (Pa·s) [defines the Newtonian plateau]

n=power law constant [defines the final slope of the high shear rateregion]

To facilitate model fitting, the power law constant is held at aconstant value. Details of the significance and interpretation of the CYmodel and derived parameters may be found in: C. A. Hieber and H. H.Chiang, Rheol. Acta, 28, 321 (1989); C. A. Hieber and H. H. Chiang,Polym. Eng. Sci., 32, 931 (1992); and R. B. Bird, R. C. Armstrong and O.Hasseger, Dynamics of Polymeric Liquids, Volume 1, Fluid Mechanics, 2ndEdition, John Wiley & Sons (1987), each of which is incorporated byreference herein in its entirety. The polymer compositions haverheological breadth parameters, i.e., “a” parameters, greater than about0.15, as determined at a temperature of 190° C. Alternatively, the “a”parameters are greater than about 0.18, greater than about 0.19, orgreater than about 0.20.

In addition, the zero shear viscosity (E_(o)) values, of the polymercompositions are less than about 10⁸ Pa·s. In one embodiment, the E_(o)values are greater than about 10⁵ Pa·s and less than about 10⁸ Pa·s. Inyet another embodiment, the E_(o) values greater than about 10⁵ Pa·s andless than about 5×10⁷ Pa·s. In still another embodiment, the E_(o)values are greater than about 10⁵ Pa·s and less than about 10⁷ Pa·s. Inanother embodiment, the E_(o) values are greater than about 10⁵ Pa·s andless than about 5×10⁶ Pa·s.

Polymer compositions having the previously described properties may beformed into articles of manufacture or end use articles using techniquesknown in the art such as extrusion, blow molding, injection molding,fiber spinning, thermoforming, and casting. For example, a polymer resinmay be extruded into a sheet, which is then thermoformed into an end usearticle such as a container, a cup, a tray, a pallet, a toy, or acomponent of another product. Examples of other end use articles intowhich the polymer resins may be formed include pipes, drums, films,bottles, fibers, and so forth. Additional end use articles would beapparent to those skilled in the art.

In an embodiment, pipes are formed from the foregoing polymercompositions using, for example, extrusion. The densities of the polymerpipes range from about 0.92 g/cc to about 0.97 g/cc. Alternatively, thedensities range from about 0.93 g/cc to about 0.965 g/cc, from about0.94 g/cc to about 0.96 g/cc, or from about 0.945 g/cc to about 0.955g/cc. Polymer density is determined in grams per cubic centimeter (g/cc)on a compression molded sample that is cooled at about 15° C. per hourand conditioned for about 40 hours at room temperature in accordancewith ASTM D1505 and ASTM D1928, procedure C.

The melt index of a polymer resin represents the rate of flow of amolten resin through an orifice of 0.0825 inch diameter when subjectedto a force of 2,160 grams at 190° C. Further, the high load melt indexof a polymer resin represents the rate of flow of a molten resin throughan orifice of 0.0825 inch diameter when subjected to a force of 21,600grams at 190° C. The MI values of the polymer pipes are in a range offrom about 0.01 g/10 min to about 10 g/10 min, alternatively from about0.1 to about 10 g/10 min. Alternatively, the polymer pipes may have MIvalues in the range of from about 0.05 g/10 min to about 5 g/10 min,from about 0.1 g/10 min to about 1.0 g/10 min, or from about 0.2 g/10min to about 0.5 g/10 min. The MI values are determined in accordancewith ASTM D1238. The polymer pipes have HLMI values in the range of fromabout 0.1 to about 100 g/10 min, from about 1 to about 10 g/10 min, fromabout 1 to about 50 g/10 min, from about 2 to about 20 g/10 min, or fromabout 4 to about 15 g/10 min. The HLMI values are determined inaccordance with ASTM D1238 condition E. In addition, the shear ratio(HLMI/MI) values of the polymer pipes are greater than about 80, greaterthan about 100, greater than about 150, or greater than about 200.

Charpy impact testing is one method of predicting the pipe's resistanceto rapid crack growth at low temperatures. In this test, compressionmolded plastic bars are cooled to various temperatures, and subjected toan impact test. The temperature at which a crack in a bar transitionsfrom ductile to brittle failure is recorded, as well as the total energyat each temperature required to break the bar. Details of the test canbe found in ASTM F2231. Results are usually reported as 1) the ductileto brittle transition temperature T_(db) (i.e., the Charpy criticaltemperature), and 2) the specific energy of breakage at a certainreference temperature, usually 0° C. (i.e., the Charpy impact energy).The lower the T_(db) and the higher the impact energy, the better theresin's resistance to rapid crack growth. The polymer pipes describedherein have a low T_(db) less than about 0° C. and a Charpy impactenergy greater than about 50 J/m. Alternatively, the T_(db) is less thanabout −5° C., less than about −10° C., or less than about −20° C.Alternatively, the Charpy impact energy is greater than about 75 J/m,greater than about 100 J/m, or greater than about 125 J/m.

The resistance of a pipe to slow crack growth is measured bypressurizing a section of a notched pipe (ASTM F1474; ISO 13479). Theresistance of a pipe material to slow crack growth is well studied anddocumented. Typically, the resistance to slow crack growth of pipeproducts improves with increasing molecular weight, decreasingcrystallinity (or density) of the starting resin, and proper placementof short chain branching in the molecular weight distribution. Theinherent resistance of a pipe to slow crack growth is measured in testssuch as the Pennsylvania notched-tensile test (PENT; ASTM F1473) usingcompression-molded specimens. Sample bars are subjected to a constantload at 80° C. until they finally break. The polymer pipes describedherein display high Pent values of greater than about 500 h, greaterthan about 700 h, or greater than about 1,000 hours.

In another embodiment, the previously described polymer compositions areblow molded into bottles. The MI values of the blow molded bottles arein the range of from about 0.01 to about 10 g/10 min, alternatively fromabout 0.1 to about 10 g/10 min. Alternatively, the blow molded bottlesmay have MI values in the range of from about 0.1 g/10 min to about 1g/10 min, from about 0.15 g/10 min to about 0.5 g/10 min, or from about0.18 g/10 min to about 0.4 g/10 min. The blow molded bottles also haveHLMI values in the range of from about 1 to about 1,000 g/10 min, fromabout 1 to about 10 g/10 min, from about 5 to about 100 g/10 min, fromabout 10 to about 80 g/10 min, from about 15 to about 50 g/10 min, orfrom about 18 to about 35 g/10 min.

Environmental Stress Crack Resistance (ESCR) measures a polymer'sresistance to chemical attack and can be determined using ASTM D 1693,condition A and condition B. For blow molded bottles having HLMI valuesranging from about 15 to about 30 g/10 min and densities greater than orequal to about 0.952, both their ESCR-A values and their ESCR-B valuesare greater than about 250, greater than about 500, greater than about800, or greater than about 1,000.

A polymer often tends to swell during blow molding extrusion. Percentweight swell measures the amount the molten resin expands immediately asit exits the die. It is a measure of the “memory” of the polymer chainsas they seek to relax and thus reform the polymer shape. Weight swell isan important parameter as it determines how tight the die gap must beadjusted to provide a constant bottle weight. If a resin has high weightswell, the die gap required will be tighter to make the proper partweight. In so doing, it will require higher stress to push the resinthrough the die than a lower weight swell resin. Weight swell is definedas the ratio of the die gap to the final bottle wall thickness. Theweight swell values of the polymer compositions described herein areusually less than about 700, less than about 500, less than about 450,or less than about 400.

As a polymer is subjected to increasing shear rates during extrusion, iteventually slips or experiences a so-called melt fracture. In anembodiment, the shear rates at the onset of melt fracture for the blowmolded polymers are greater than about 22,000/sec. Alternatively, theshear rates are greater than about 24,000/sec, greater than about26,000/sec, or greater than about 28,000/sec.

EXAMPLES

The invention having been generally described, the following examplesare given as particular embodiments of the invention and to demonstratethe practice and advantages thereof. It is understood that the examplesare given by way of illustration and are not intended to limit thespecification or the claims to follow in any manner.

Example 1

A grade 963 chromium oxide/silica-titania catalyst obtained from W.R.Grace Corporation was activated in air at 800° C. To activate thecatalyst, about 10 grams were placed in a 1.75 inch quartz tube fittedwith a sintered quartz disk at the bottom. While the catalyst wassupported on the disk, dry air was blown up through the disk at thelinear rate of from about 1.6 to about 1.8 standard cubic feet per hour.An electric furnace around the quartz tube was then turned on and thetemperature was raised at the rate of 400° C. per hour to the indicatedtemperature, i.e., 800° C. At that temperature the catalyst was allowedto fluidize for three hours in the dry air. The temperature was thenlowered to 350° C. where the air was flushed out with dry nitrogen, andthen the catalyst was reduced in the presence of carbon monoxide (CO)for 30 minutes. After a final flushing out of the CO with nitrogen, thecatalyst was collected and stored under dry nitrogen, where it wasprotected from the atmosphere until ready for testing. It was neverallowed to experience any exposure to the atmosphere.

The catalyst was then employed in four different runs to polymerizeethylene. The polymerization runs were made in a 2.2 liter steel reactorequipped with a marine stirrer running at 400 rpm. The reactor wassurrounded by a steel jacket containing boiling methanol and connectedto a steel condenser. The boiling point of the methanol was controlledby varying nitrogen pressure applied to the condenser and jacket, whichpermitted precise temperature control to within half a degreecentigrade, with the help of electronic control instruments.

Unless otherwise stated, a small amount (normally 0.01 to 0.10 grams) ofthe catalyst was first charged under nitrogen to the dry reactor. Next0.6 liter of isobutane liquid was added to the reactor, followed by asolution containing the non-transition metal Cp cocatalyst, and finallyby another 0.6 liter of isobutane liquid. Then the reactor was heated upto 95° C., followed by the addition of 30 psig of hydrogen gas (H₂).Finally ethylene was added to the reactor to equal a fixed pressure of550 psig. The reaction mixture was stirred for about one hour. Asethylene was consumed, more ethylene flowed into the reactor to maintainthe pressure. The activity was noted by recording the flow of ethyleneinto the reactor to maintain the set pressure.

After the allotted time, the ethylene flow was stopped and the reactorwas slowly depressurized and opened to recover a granular polymerpowder. In all cases, the reactor was clean with no indication of anywall scale, coating, or other forms of fouling. The polymer powder wasthen removed and weighed. The activity was specified as grams of polymerproduced per gram of solid oxide component charged per hour.

Run 1 was performed in the absence of a cocatalyst, runs 2 and 3 wererun using different amounts of the trimethylsilylcyclopentadienyllithium (TMS-Cp-Li) as a cocatalyst, and run 4 was run usingbiscyclopentadienyl magnesium (Cp₂Mg) as a cocatalyst. Table 1 belowprovides details regarding each run and the MI, HLMI, HLMI/MI, M_(N),M_(W), and PDI values of the polymer resin produced in each run. Themethods used to determine such values are disclosed above. As shown inTable 1, the MI and HLMI values increased substantially when anon-transition metal Cp cocatalyst was used with H₂. When used withoutH₂, the melt index actually dropped, thus supporting the theory thatchromocenyl sites form on the catalyst when the cocatalyst and H₂ areused. In addition, the breadth of the MWD, i.e., the PDI, increased whenthe cocatalyst was used with H₂.

Example 2

A 969 MPI grade Cr/silica-titania catalyst was obtained from W.R. Graceand activated in air at 650° C. in the same manner as described inExample 1. It was then reduced in the presence of CO at a temperature ofabout 370° C. The catalyst was then employed in several runs topolymerize ethylene at 95° C. as described in Example 1. Most but notall of the runs were performed in the presence of H₂. Some runs wereperformed using no cocatalyst, and some runs were performed using Cp₂Mgcocatalyst, one of which additionally used triethylaluminum (TEA)cocatalyst. Other runs were performed using CpLi cocatalyst. Table 2below provides details regarding each run and the MI, HLMI, HLMI/MI,M_(N), M_(W), and PDI values of the polymer resins produced in each run.The methods used to determine such values are disclosed above. As shownin Table 2, the MI and HLMI values generally increased when anon-transition metal Cp cocatalyst was used with H₂. In addition, thebreadth of the MWD, i.e., the PDI, increased when the cocatalyst wasused with H₂.

Example 3

A 963 grade Cr/silica-titania catalyst obtained from W.R. Grace Corp.,was calcined in air at 650° C. as described above in Example 1. It wasthen reduced in the presence of CO at a temperature of about 370° C. Thecatalyst was then employed in two different runs to polymerize ethyleneas described in Example 1. One run was performed in the absence of acocatalyst and in the absence of H₂. The other run was performed usingCp₂Mg as a cocatalyst and in the presence of H₂. Table 3 below providesdetails regarding each run and the MI, HLMI, HLMI/MI, M_(N), M_(W), andPDI values of the polymer resin produced in each run. The methods usedto determine such values are disclosed above. As shown in Table 3, theMI and HLMI values increased substantially when the Cp₂Mg cocatalyst wasused with H₂. In addition, the breadth of the MWD, i.e., the PDI,increased when the cocatalyst was used with H₂.

Example 4

A 969 MPI grade Cr/silica-titania catalyst was obtained from W.R. GraceCorp. and calcined in air at 650° C. as described in Example 1. Thecatalyst and 4 ppm of Cp₂Mg cocatalyst based on the weight of theisobutane added were then employed in three runs to polymerize ethylenein the presence of H₂ at 95° C. and 30 psig. The catalyst was reduced inthe presence of CO at a temperature of about 371° C. before two of thethree runs. A triethylaluminum cocatalyst was additionally used in oneof these runs. The catalyst and the cocatalyst(s) were suspended in anisobutane diluent within a pipe loop reactor during these differentruns. Table 4 below provides details regarding each run and the MI,HLMI, HLMI/MI values of the polymer resins produced in each run. Themethods used to determine such values are disclosed above. These valuesimproved when TEA cocatalyst was used to supplement the Cp₂Mg catalyst.In the run in which the catalyst had not been reduced beforehand, thecatalyst exhibited little activity.

TABLE 1 Non- Catalyst Run MI HLMI Transition Metal Charge Yield TimeProd. Activity (g/10 (g/10 HLMI/ M_(N) M_(W) Run # Cp Treatment (g) (g)(min.) (g/g) (g/g/h) min.) min.) MI (kg/mol) (kg/mol) PDI 1 none 0.045269.5 74.5 1538 1238 0.12 7.6 63 15.4 165.2 10.7 2 4 ppm TMS-Cp-Li 0.1796279 54 1553 1726 0.18 25.4 141 6.3 367.5 58.2 3 11.3 ppm TMS-Cp-Li0.1176 155 50 1318 1582 0.945 107.6 114 5.1 238.5 46.6 4 4 ppm Cp₂Mg0.0891 74.5 77.1 836 651 1.58 224.3 142 4.3 255.0 59.3

TABLE 2 Non- Transition H₂, Catalyst Run MI HLMI Metal Cp psig on ChargeYield Time Prod. Activity (g/10 (g/10 HLMI/ M_(N) M_(W) Run # TreatmentRx (g) (g) (min.) (g/g) (g/g/h) min.) min.) MI (kg/mol) (kg/mol) PDI 5none 0 0.0536 133 62 2481 2401 0 0.4 32.8 724.4 22.0 6 none 30 0.0848267 68 2624 2315 0 0.81 33.4 641.0 19.2 7 1 ppm Cp₂Mg 30 0.1054 208 601973 1973 0 0.95 21.7 812.3 37.5 8 2 ppm Cp₂Mg 30 0.1045 143 70 13681173 0 2.05 15.6 851.2 54.7 9 4 ppm Cp₂Mg 30 0.0798 61 64 764 717 0 4.613.0 753.6 58.0 10 5.4 ppm Cp₂Mg 30 0.1042 50 60 480 480 0.017 6.92 40710.2 574.9 56.4 11 4 ppm Cp₂Mg + 30 0.0998 105 65 1052 971 0.033 8.7 26310.4 554.5 53.2 8 ppm TEA 12 6 ppm Cp₂Mg 0 0.0982 50 60 509 509 0 0 13 1ppm CpLi 30 0.0942 61 68 648 571 0 1.52 20.2 675.4 33.5 14 4 ppm CpLi 300.1014 27 63 266 254 0 2.84

TABLE 3 Non- Transition H₂, Catalyst Run MI HLMI Metal Cp psig on ChargeYield Time Prod. Activity (g/10 (g/10 HLMI/ M_(N) M_(W) Run # TreatmentRx (g) (g) (min.) (g/g) (g/g/h) min.) min.) MI (kg/mol) (kg/mol) PDI 15none 0 0.0436 168 94 3853 2459 0 0.79 20.2 736.0 36.4 16 1 ppm Cp₂Mg 300.0566 70 60 1237 1237 0.0254 6.55 258 7.2 838.5 116.3

TABLE 4 Catalyst Run MI HLMI CO Other Charge Yield Time Prod. Activity(g/10 (g/10 HLMI/ Run # Reduction Cocatalyst (g) (g) (min.) (g/g)(g/g/h) min.) min.) MI 17 none none 0.0873 2 53 23 26 18 371C none0.0798 61 64 764 717 0 4.6 19 371C 8 ppm TEA 0.0998 105 65 1052 9710.033 8.7 263

Example 5

A 963 grade Cr/silica-titania catalyst was calcined in air at 800° C.and reduced in the presence of CO at a temperature of about 370° C., asdescribed in Example 1. The catalyst was then employed in threedifferent runs to polymerize ethylene in the presence of H₂ at 95° C.and 30 psig, again as described in Example 1. A first run was performedusing TMS-Cp-Li as the cocatalyst, a second run was performed usingCp₂Mg as the cocatalyst, and a third run was performed using nococatalyst. FIG. 1 illustrates the molecular weight distributions of thepolymer resins produced in these runs. The breadths of the molecularweight distributions of the polymer resins produced using thenon-transition metal Cp cocatalysts were greater than that of thepolymer resin produced in the absence of such cocatalyst. They were alsoshifted to the left, indicating an exaggerated effect of H₂ due to theinfluence of the Cp compound.

Example 6

A 969 MPI Cr/silica-titania catalyst was calcined in air at 650° C. asdescribed in Example 1. It was then reduced in the presence of CO at atemperature of about 370° C. The catalyst was then employed in severalruns to polymerize ethylene in the presence of H₂ at 95° C. and 30 psig,again as described in Example 1. All runs but one were performed usingCp₂Mg cocatalyst, and one additional run was performed using 8 ppm ofTEA cocatalyst along with the Cp₂Mg cocatalyst. FIG. 2 illustrates themolecular weight distributions of the polymer resins produced in theseruns. Again, the breadths of the molecular weight distributions of thepolymer resins produced using the non-transition metal Cp cocatalystswere greater than that of the polymer resin produced in the absence ofsuch cocatalyst. They were also shifted to the left, indicating theeffect of H₂.

Example 7

A 969 MPI grade Cr/silica-titania catalyst was calcined in air at 600°C. and reduced in the presence of CO at a temperature of about 370° C.as described in Example 1 The catalyst was then employed in twodifferent runs to polymerize ethylene in the presence of H₂ at 95° C.and 30 psig as described in example 1. A first run was performed usingCpLi as the cocatalyst, and a second run was performed using nococatalyst. FIG. 3 illustrates the molecular weight distributions of thepolymer resins produced in these runs. The breadth of the molecularweight distribution of the polymer resin produced using the CpLicocatalyst was slightly greater than that of the polymer resin producedin the absence of such cocatalyst. Again, it was shifted to the left,indicating that the effect of H₂ was exaggerated by the cocatalyst.

Example 8

The following procedure was followed to produce polymer resins in apilot plant reactor. Larger quantities of grade 964 Cr/silica-titaniacatalyst than in previous examples were activated by calcination in airat 650° C. for use in a 23-gallon loop reactor. Then 1.5 pounds of thecatalyst were charged to a 6-inch diameter stainless steel furnace,which was heated by electric heating coils surrounding it. Dry air roseup through a sintered metal grid plate at the rate of 0.12 to 0.20linear feet per second to fluidize the catalyst. The catalyst was heatedup to the desired temperature, i.e., 650° C. in this example, over aperiod of about five hours. It was held at that temperature for anothersix hours. The catalyst was given a final treatment in carbon monoxide(CO) before being discharged from the furnace and stored under nitrogen.This was done in order to reduce the hexavalent chromium to its divalentstate. This was accomplished by cooling down the catalyst from 650° C.to 370° C. while fluidizing the catalyst in dry air. The air was thenreplaced by nitrogen for about 10 minutes, and then about 10% CO byvolume of the total gas was added. This CO treatment lasted 1 hour,after which the catalyst was flushed clean with nitrogen for about 1hour and cooled down to room temperature and stored under dry nitrogenuntil being used. About 65% to 85% of the catalyst weight charged wasrecovered. The lost weight was water and very fine material.

While the original hexavalent catalysts were usually orange or yellow,this reduced divalent catalyst appeared blue and chemiluminescedbrightly when exposed to oxygen.

The activated catalyst was employed in various runs with differentamounts of Cp₂Mg cocatalyst to polymerize ethylene that had been driedover activated alumina. Liquid isobutane that had been degassed byfractionation and dried over alumina was used as the diluent.

The reactor was a 15.2 cm diameter pipe loop filled with liquid andhaving a volume of 23 gallons (87 liters). The reactor pressure wasabout 600 psig. The reactor temperature was varied over the range of 88°C. to 94° C. The reactor was operated to have a residence time of 1.25hours. The catalyst was added through a 0.35 cc circulating ball-checkfeeder. At steady state conditions the isobutane feed rate was about 46L/hr and the ethylene feed rate was about 30 lbs/hr. The ethyleneconcentration in the diluent was 8 to 12 mole %. Hydrogen was added inconcentrations ranging from 0.4 to 1.1 mole % based on the total molesof the diluent. The Cp₂Mg cocatalyst was added in concentrations rangingfrom 0.25 to 1.1 parts per million by weight of the diluent. The Cp₂Mgcocatalyst was added as a hydrocarbon stream into a pre-contactingvessel into which the catalyst was also added continuously. Theisobutane flow through the pre-contacting vessel was adjusted so thatthe contact time between the catalyst and cocatalyst was about 20minutes on average. After that amount of time, the contacted catalystand cocatalyst are then fed into the reactor. To prevent static buildupin the reactor, a small amount (<5 ppm of diluent) of STADIS 450antistatic agent sold by Octel Corp. was usually added. The polymer wasremoved from the reactor at a rate of about 25 lbs/hour and recovered ina flash chamber. A Vulcan dryer was used to dry the polymer undernitrogen at about 60 to 80° C.

The polymers produced in these runs were blown into 1 mil (0.001inch)-thick films on a high density processing line. The line used was a1.5 inch diameter Davis-Standard extruder with L/D of 24:1, having abarrel temperature of from 210° C. to 230° C., a screw speed of 30 rpm,and an output of 17 to 18 pounds per hour, feeding a 2 inch diameterSano die having a 35 mil gap. Films of typically 0.001-0.0005 inch (1 to0.5 mil) thickness were blown on a 4:1 blow-p ratio and a productionrate of 65 ft/min. Frostline heights were usually 14 inches. Aftercooling, the film passed through an A-frame with a resultant flattenedwidth of 12.5 inches.

Various properties of the films produced using the Cp₂Mg cocatalyst weretested and compared to the same properties of a 1 mil (0.001 inch) thickfilm produced from a commercial high density film resin sold by ChevronPhillips Chemical Company LLC and its licensees as TR-130 resin. Theresults of these tests are shown in Table 5 below. In particular, thedensity and melt index of each film resin was determined in the mannerdescribed previously. Each film was subjected to the dart impact test inaccordance with ASTM D 1709-75. The dart impact test is a standard testmethod for determining the impact resistance of polyethylene films. Itis the energy needed to rupture a one millimeter thick film upon impactof a free falling dart. This method establishes the weight of the dartdropped from a height of 26 inches, which causes 50% of the samples tobreak. All but one of the Cp₂Mg produced films had dart impacts higherthan or comparable to the TR-130 produced film. Another measure of filmtoughness is the Spencer Impact resistance (also known as the pendulumimpact strength). The Spencer Impact resistance of each film was alsodetermined in accordance with ASTM D 3420. These values of the Cp₂Mgproduced films were higher than or similar to that of the TR-130produced film.

Each film was further subjected to a tear resistance test in accordancewith ASTM D 1922. This test is a standard test method for determiningthe propagation tear resistance of a polymer film and is a modificationof the Elmendorf tear test used for paper. The method determines theaverage energy in grams required to propagate a tear through 2.5 inchesof film in the machine extrusion direction (MD) or transverse direction(TD) as indicated. The MD and TD tear resistances of the Cp₂Mg producedfilms were substantially higher than those of the TR-130 produced film.

Table 5 also shows the motor load in amperes and the die pressure inpsig generated while processing the film. They indicate the amount ofresistance the molten polymer offered against the screw. One can seethat the polymers produced with a metal Cp cocatalyst in generalprocessed with greater ease than the control polymer, even though manyof them had higher melt viscosity values (lower melt index values). Theease of processing can determine the rate at which film can be processedand thus the capacity of a film line.

Example 9

As shown in Table 6, Cr/silica-titania catalyst grades 963 and 964 fromW.R. Grace were used to produce polymer resins in a pilot plant reactoras described above in Example 8. The catalysts were activated at 600° C.and 650° C., followed in many cases by reduction in CO at 370° C. Thereactor temperature was 82 to 91° C., the ethylene concentration was 10to 14% by moles of the diluent, and the hydrogen concentration was 0.3to 0.4% by moles of the diluent. As indicated in Table 6, a Cp₂Mgcocatalyst was used in most of the runs in concentrations ranging from0.25 to 1 ppm based on the weight of the diluent. However, one run wasperformed with no cocatalyst and another run was performed with TEB asthe cocatalyst.

The polymer resins produced in these runs were extruded into pipes. Thepipe extrusion was performed by melting and conveying polyethylenepellets into an annular shape and solidifying that shape during acooling process. All pipe products tested in this study were made usinga 2 inch Davis-Standard Single Screw Extruder (smoothbore) and a 220° C.set temperature on the extruder and die. The samples were extruded at150 lb/hr using a Barrier screw. The melt temperatures ranged from 232to 238° C. A two inch die was used. To cool the pipe and “freeze in” thedesired dimensions, cooling was accomplished by the use of several watertanks where the pipe was sprayed with water on the pipe exterior. Thus,the pipe was cooled from the outside surface to the inside surface. PerD2513 “Standard Specification for Thermoplastic Gas Pressure Pipe,Tubing, and Fittings”, the maximum wall thickness eccentricity is 12%and the maximum ovality is 5%. The resins produced using metal Cpcocatalysts fell within those values.

A TR-480 pipe resin sold by Chevron Phillips Chemical Company and madefrom a chromium-based catalyst was tested as the control. Also, an H516polyethylene resin sold by Chevron Phillips Chemical Company was testedas a control. It was made using a Ziegler-Natta catalyst in a bimodalprocess. A third control resin was produced using the same catalyst buta different cocatalyst, i.e., triethylboron, was used.

Various properties of the pipes were tested, and the results of thesetests are shown in Table 6. The HLMI, density, M_(W), M_(N), and PDI ofeach resin, and the Charpy critical temperature, Charpy energy, and PENTof each pipe were tested using the methods described previously.Normally PENT increases as the density of the resin decreases. However,one can see in the table that some of the polymers described herein,despite having higher densities, also have higher PENT values than thecontrol resins that are even equivalent to the bimodal grade H516 resin,which is more difficult to make and to process into pipe. The Charpycritical temperatures were also much lower for the polymers describedherein, which indicates high resistance to rapid crack propagation. Thetotal energy adsorbed (at 25° C. Charpy Impact) was also very high forall of the polymers described herein relative to the control resins.

Standard PE-100 screening hoop stress tests were also run on thesepolymers. In this test, a two foot length of pipe was pressured to theindicated pressure and then immersed in a water bath set at theindicated temperature. The duration of time that each pipe lasted (theaverage of three) was then recorded.

Example 10

A grade 964 Cr/silica-titania catalyst from W.R. Grace was used toproduce polymer resins in a pilot plant reactor as described above inExample 8. The catalyst was activated at 650° C. and reduced in thepresence of CO at a temperature of about 370° C. The catalyst wasemployed with different amounts of the Cp₂Mg cocatalyst in various runsto polymerize ethylene at 94 to 102° C. in the presence of 0.3 to 0.4mol % H₂ based on the isobutane diluent. The ethylene content in thereactor was 10 mol % ethylene based on the isobutane diluent. Theresulting polymers and their properties are shown in Table 7.

The polymers produced are useful for blow molding applications. Blowmolding evaluations were conducted by blowing a one gallon (105.1 grams)bottle on a UNILOY 2016 single head blow molding machine (sold by UniloyMilacron Inc.) using a 2.5 inch diameter die, 20 degree diverging die,32% accumulator position, 8.5 second blow time, 0.10 second blow delay,0.75 second pre-blow delay and a 45° F. mold temperature. Areciprocating screw speed of 45 rpm was used, providing parisonextrusion at shear rates greater than 10,000/sec through the die.

The polymers' ease of processing during blow molding was determinedusing known measurements. The first measure, listed as “Output” in Table7, was calculated from the cycle time of the machine and the weight ofthe bottle and flashing. This measure describes the rate of bottleoutput in lbs of polymer per hour at which the resin in question wasblow molded into bottles during normal operation, and it would describethe commercial rate of bottle production. The second measure was thecycle time, i.e., the time needed to make the bottle and was measured inseconds. Another measure of processing ease is the head pressure, whichmeasures the maximum pressure at the die plate during the extrusion ofthe bottle. In other words, it is the pressure at the die plate as thebottles are being blown.

The previously discussed weight swell values for the polymers duringblow molding were also determined as shown in Table 7. Anothermeasurement of the swell is the die swell or the diameter swell, whichis the ratio of the parison diameter to the die diameter. These numberswere referenced to a standard commercial blow molding polyethylene resinknown as MARLEX® 5502BN resin, which was obtained from Chevron PhillipsChemical Company.

The onset of melt fracture of each resin was evaluated on the sameUNILOY machine by opening the die gap and extruding the resin. The shearrate was increased steadily by increasing the screw rpm. The onset wasthe rpm at which the parison showed visible signs of melt fracture, suchas a shark skin appearance or a distorted surface. This rate was thentranslated into the shear rate listed in Table 7. A high value indicatedthat the polymer could be processed at high rates without melt fracture.

Environmental stress crack resistance was also tested using ten 1-gallonbottles made as described above on a UNILOY 2016 machine. The bottleswere filled with a 10% Orvus-K detergent solution, capped, and placed ina 140° F. hot room. Bottle failures were noted each day until all hadbroken, and a 50% mean failure time was calculated for each set.

The bottle toughness of the ten 1-gallon bottles was measured by theIzod impact test (Izod Impact, notched (kJ/m2): ASTM D256(a)-84). Ahigher number indicated greater toughness. Drop impact tests were alsoperformed to measure bottle toughness by filling the 1-gallon bottlescompletely full of water and then sealing the bottles by means of ascrew cap. These liquid filled bottles were then dropped from a verticalposition onto a flat surface from progressively higher levels up to 12feet high or until the bottle ruptured upon impact. A new bottle wasused for each drop.

Based on the results shown in Table 7, various properties of the bottlesproduced using the Cp₂Mg cocatalyst (the polymers disclosed herein) werefound to be superior when compared to the same properties of bottlesproduced from the standard MARLEX® HHM 5502BN polyethylene resin sold byChevron Phillips Chemical Company. This resin, which has been sold for35 years, has become a standard of the industry because of its excellentprocessing characteristics. However, one can see in Table 7 from thecycle times, output rates, melt fracture shear rates, and head pressurethat the polymers disclosed herein processed better. One can also seethat the polymers disclosed herein had superior ESCR and impactproperties. Their ESCR values were more than ten times greater thanthose values for the MARLEX® HHM 5502BN resin. The polymers disclosedherein further exhibited a lower swell.

A commercially available resin known as ALATHON® L54400S bimodal resin,which is sold by Equistar Chemicals, LP, was also compared. This bimodalresin is known for its high ESCR. The results in Table 7 below indicatethat the polymers produced using the metal Cp cocatalyst also exhibitedhigh ESCR values. In fact, both the ASTM ESCR values and the bottle ESCRof these polymers were quite surprising. The Izod impact and bottle dropproperties of the polymers produced using the metal Cp cocatalyst werealso very good compared to the control resins.

TABLE 5 Resin 1 2 3 4 5 6 MgCp₂ Added (ppm) 0.25 0.25 0.5 1.1 1.1Commercial TR130 Density (g/cc) 0.937 0.936 0.937 0.938 0.934 0.937 MI(g/10 min) 0.31 0.33 0.28 0.29 0.16 0.28 M_(N) (kg/mol) 13.97 10.0515.67 7.1 10.14 13.8 M_(W) (kg/mol) 197.49 226.16 114.23 168.41 283.86227.00 M_(W)/M_(N) 14.14 22.50 7.29 23.72 28.0 16.5 Eta(0) (Pa · s)3.08E+05 5.13E+05 8.65E+05 1.36E+06 2.95E+06 4.56E+05 Tau (s) 6.75E−011.34E+00 2.40E+00 8.07E+00 1.45E+01 1.34 CY-“a” parameter 1.75E−010.1606 1.55E−01 1.57E−01 0.1473 0.1729 Dart Impact (g) 83 80 90 50 11381 Spencer Impact (J) 0.45 0.63 0.48 0.51 0.91 0.45 MD Tear Resistance(g) 63 100 59 89 70 52 TD Tear Resistance (g) 704 712 843 781 918 672Pressure (psig) 1600 1150 1150 1100 1250 1200 Motor Load (amp) 5.7 5.15.1 4.1 5.6 5.9

TABLE 6 Sample 7 8 9 10 11 12 13 14 Catalyst 964, 650° C. 963, 650° C.964, 650° C. 964, 650° C. 964, 650° C. 963, 600° C. 963, 600° C. H516 COReduced CO Reduced CO Reduced CO Reduced CO Reduced Cp₂Mg added 0.25 ppm1 ppm 0.5 ppm 1 ppm 1 ppm none 5 ppm TEB ZN Bimodal HLMI 6.7 5.4 6.9 1011 10 8.5 8 (g/10 min.) Density (g/cc) 0.9503 0.9502 0.9497 0.94900.9539 0.945 0.9503 0.95 M_(W) 377.05 511.37 417.88 466.25 472.18 243.3319.6 256.5 (kg/mol) M_(N) 14.06 10.14 11.42 8.57 7.96 22.5 8.72 20.1(kg/mol) PDI 27 50 37 54 59 16.8 36.7 12.8 Eta(0) (Pa · s) 4.08 ×10{circumflex over ( )}6 2.62 × 10{circumflex over ( )}7 5.78 ×10{circumflex over ( )}6 1.50 × 10{circumflex over ( )}7 2.49 ×10{circumflex over ( )}7 1.54 × 10{circumflex over ( )}6 4.6 ×10{circumflex over ( )}6 2.74 × 10{circumflex over ( )}5 Tau (s) 26.8 4853 269 537 5.2 55 1.9 CY-“a” parameter 0.1840 0.1965 0.1918 0.18890.1815 0.1629 0.205 0.3093 Charpy Critical Temp.° C. −24.2 −24.3 −25.3−3.0 −2.4 −3.4 −4.4 −22.0 Total Energy at 128 144 144 98 86 36 69 12923° C. (J/m) PENT (h) 27 (D) >750 84 (D) >750 >750 13 456 >750 HoopStress 20° C., 12.4 (Mpa) 30, 44, 67 35, 66, 92 63, 116, 157 1000 36 65(D) (D) (D) 80° C., 5.5 (Mpa) 25, 137, 163 130, 183, 197 2, 3, 8 200 22932 (D) (B) (B)

TABLE 7 MARLEX HHM ALATHON Resin ID 5502BN L54400S Sample 15 16 17 18 19Cp₂Mg (ppm) 1.1 0.5 0.5 MI (g/10 min) 0.39 0.34 0.15 0.19 0.21 HLMI(g/10 min) 34.98 33.08 22.56 18.81 21.10 HLMI/MI 89.7 97.3 150.4 99.0100.5 Density (g/cc) 0.9537 0.9545 0.9530 0.9499 0.9536 M_(W) (kg/mol)168.52 191.55 413.7 329.0 340.6 M_(Z) (kg/mol) 2143 1869 8788 6748 6617PDI 8.042 10.475 37.148 24.745 25.730 E_(o) (Pa · s) 621600 148600014280000 1566000 1365000 T_(ξ) (s) 1.348 2.323 151.1 5.948 5.338 CY-“a”parameter 0.1432 0.1254 0.1348 0.1525 0.1539 0.1667 Notched Izod(ft-lb/in) 2.295 P 1.572 P 1.609 P 2.133 P 2.237 P Tensile Impact(ft-lb/in²) 53.4 71.9 62.0 75.3 69.0 ESCR A, F50 (hr) 34142 >1000 >1000 >1000 ESCR B, F50 (hr) 31 124 >1000 >1000 >1000 BottleESCR, (hr) 213 165 >1175 >1175 >1175 10% Joy F50 Bottle Drop Impact(ft) >12 10.5 10.7 11.5 >12 Part Weight (g) 168 161 179 157 153 CycleTime (s) 11.7 11.6 15.5 11.4 11.8 Die Gap (in) 0.0159 0.0200 0.01200.0154 0.0151 Weight Swell (%) 450 320 676 433 429 Diameter Swell (%)33.6 32.4 39.0 36.0 41.6 Melt Temperature (° F.) 381 381 381 381 381Head Pressure (psi) 5160 4650 5360 5730 5700 Output (lb/hr) 113.9 110.191.6 109.2 102.8 Shear Rate (l/s) 26274 15770 29298 23890 25863 Resin IDSample 20 21 22 23 Cp₂Mg (ppm) 0.25 0.25 0.25 0.25 MI (g/10 min) 0.200.31 0.31 0.31 HLMI (g/10 min) 16.63 21.44 21.00 19.54 HLMI/MI 83.2 69.267.7 63.0 Density (g/cc) 0.9535 0.9548 0.9540 0.9541 M_(W) (kg/mol)337.7 253.0 230.4 258.2 M_(Z) (kg/mol) 7112 4233 2937 3783 PDI 21.11914.939 13.993 15.341 E_(o) (Pa · s) 717700 289400 325600 419000 T_(ξ)(s) 2.119 0.633 0.6893 0.9632 CY-“a” parameter 0.1432 0.1754 0.17140.1689 0.1432 Notched Izod (ft-lb/in) 2.848 P 2.775 P 2.719 P 2.524 PTensile Impact (ft-lb/in²) 97.0 78.6 75.9 72.4 ESCR A, F50 (hr) 506 183269 259 ESCR B, F50 (hr) 722 154 244 310 Bottle ESCR, (hr) 832 647 991439 10% Joy F50 Bottle Drop Impact (ft) >12 >12 >12 >12 Part Weight (g)160 164 157 158 Cycle Time (s) 11.4 11.4 11.4 11.5 Die Gap (in) 0.01740.0166 0.0161 0.0166 Weight Swell (%) 378 414 408 396 Diameter Swell (%)47.7 48.5 47.7 46.7 Melt Temperature (° F.) 381 382 381 381 HeadPressure (psi) 5570 5370 5440 5370 Output (lb/hr) 111.3 114.1 109.2108.9 Shear Rate (l/s) 20185 22308 23582 22731

While preferred embodiments of the invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the invention. Theembodiments described herein are exemplary only, and are not intended tobe limiting. Many variations and modifications of the inventiondisclosed herein are possible and are within the scope of the invention.Use of the term “optionally” with respect to any element of a claim isintended to mean that the subject element is required, or alternatively,is not required. Both alternatives are intended to be within the scopeof the claim.

Accordingly, the scope of protection is not limited by the descriptionset out above but is only limited by the claims which follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated into the specification as an embodiment ofthe present invention. Thus, the claims are a further description andare an addition to the preferred embodiments of the present invention.The discussion of a reference herein is not an admission that it isprior art to the present invention, especially any reference that mayhave a publication date after the priority date of this application. Thedisclosures of all patents, patent applications, and publications citedherein are hereby incorporated by reference, to the extent that theyprovide exemplary, procedural, or other details supplementary to thoseset forth herein.

1. A polymer of ethylene and hexene having a HLMI in a range of fromabout 15 g/10 min to about 50 g/10 min, a density greater than about0.952 g/cc, an ESCR condition A greater than about 250 hours, and arheological breadth parameter of from 0.15 to 0.20.
 2. The polymer ofclaim 1, wherein the ESCR condition A is greater than about 500 hours.3. The polymer of claim 1, wherein the ESCR condition A is greater thanabout 1000 hours.
 4. The polymer of claim 1, wherein the density isgreater than about 0.954 g/cc.
 5. The polymer of claim 1, wherein thedensity is greater than about 0.954 g/cc, and the ESCR condition A isgreater than about 1,000 hours.
 6. The polymer of claim 1 having an ESCRcondition B greater than about 500 hours.
 7. The polymer of claim 1having an ESCR condition B greater than about 1000 hours.
 8. The polymerof claim 1 having an ESCR condition B greater than about 1,000 hours,wherein the density is greater than about 0.954 g/cc.
 9. A polymer ofethylene and hexene having a HLMI in a range of from about 15 g/10 minto about 50 g/10 min, an ESCR condition A greater than about 800 hours,weight swell less than about 700%, and a rheological breadth parameterof from 0.15 to 0.20.
 10. The polymer of claim 9, wherein the weightswell is less than about 500%.
 11. The polymer of claim 9 having anonset of melt fracture greater than about 24,000/sec.
 12. The polymer ofclaim 10 having an onset of melt fracture greater than about 24,000/sec.13. The polymer of claim 9, wherein the ESCR condition A is greater thanabout 1000 hours.
 14. The polymer of claim 9 having an onset of meltfracture greater than about 24,000/sec, wherein the weight swell is lessthan about 500%, and wherein the ESCR condition A is greater than about1,000 hours.
 15. The polymer of claim 14, wherein the polymer has aCharpy impact energy of greater than about 100 J/m.
 16. The polymer ofclaim 9, wherein the weight swell is less than that exhibited by thecommercial resin HHM 5502 when molded under control conditions.
 17. Apolymer of ethylene and hexene having a HLMI in a range of from about 15g/10 min to about 50 g/10 min, an ESCR condition A greater than about800 hours, an onset of melt fracture greater than about 26,000/sec, anda rheological breadth parameter of from 0.15 to 0.20.
 18. The polymer ofclaim 17, wherein the onset of melt fracture is greater than about28,000/sec.
 19. The polymer of claim 17, wherein the onset of meltfracture greater is than that exhibited by the commercial resin HHM 5502when molded under control conditions.
 20. A polymer composition having aweight average molecular weight (M_(W)) greater than about 100,000g/mol, a high load melt index (HLMI) in a range of from about 4 g/10 minto about 15 g/10 min, a critical temperature (T_(c)) of less than about−15° C., a zero shear viscosity (E_(o)) less than about 10⁷ Pa·s, and arheological breadth parameter of from 0.15 to 0.20.
 21. The polymer ofclaim 1, having rheological breadth parameter of from about 0.16 toabout 0.20.
 22. The polymer of claim 1, having rheological breadthparameter of from about 0.16 to about 0.19.